Dynamic recrystallization in lead
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Fig. 1-Stress-strain curves exhibiting dynamic recrystallization at high and low strain rates.
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Dynamic Recrystallization in Lead
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J. H. NICHOLLS AND P. G. MCCORMICK
METALSwhich
recrystallize during deformation exhibit s t r e s s - s t r a i n c u r v e s at low s t r a i n r a t e s which o s c i l l a t e p r i o r to the e s t a b l i s h m e n t of a s t e a d y s t a t e flow s t r e s s , t-4 The extent and a m p l i t u d e of the flow s t r e s s o s c i l l a t i o n d e c r e a s e s with i n c r e a s i n g s t r a i n r a t e until, at high s t r a i n r a t e s , only a s i n g l e flow s t r e s s peak i s o b s e r v e d . Luton and S e l l a r s 4 h a v e r e c e n t l y shown that the change in f o r m of the s t r e s s - s t r a i n c u r v e with i n c r e a s i n g s t r a i n r a t e is due to the r e l a t i v e m a g n i t u d e and s t r a i n r a t e d e p e n d e n c e of the c r i t i c a l s t r a i n f o r r e c r y s t a l l i z a t i o n , ~c, and the s t r a i n o c c u r ing d u r i n g the r e c r y s t a l l i z a t i o n of a l a r g e f r a c t i o n of the s p e c i m e n , ~x- At low s t r a i n r a t e s p e r i o d i c r e c r y s t a l l i z a t i o n c y c l e s will o c c u r if Cc > Cx, s i n c e , at l e a s t i n i t i a l l y , e a c h r e c r y s t a l l i z a t i o n c y c l e will e s s e n t i a l l y be c o m p l e t e d p r i o r to the i n i t i a t i o n of the next c y c l e . If the r a t e of i n c r e a s e of Cx with s t r a i n r a t e is g r e a t e r than that of ec, then at a s u f f i c i e n t l y high s t r a i n r a t e , ex > ~c, and s u c c e s s i v e r e c r y s t a l l i z a t i o n c y c l e s will o v e r l a p , l ead i n g to a continuous r e c r y s t a l l i z a t i o n p r o c e s s . T h i s was v e r i f i e d in n i c k e l t e s t e d in hot t o r s i o n , 4 w h e r e the t r a n s i t i o n f r o m p e r i o d i c to continuous b e h a v i o r was found to o c c u r at Cx -~ Cc. In the p r e s e n t w o r k the t r a n s i t i o n f r o m p e r i o d i c to continuous d y n a m i c r e c r y s t a l l i z a t i o n in lead has b e e n studied. C o m m e r c i a l p u r i t y (99.99 p c t Pb) lead w a s u s e d in this study. The t e n s i l e s p e c i m e n s w e r e in the f o r m of J. H. NICHOLLS, formerly Student, School of Metallurgy, University of New South Wales, Kensington, NSW, Australia, is with Australian Iron and Steel, Port Kembla, NSW. P. G. MCCORMICKis Lecturer, School of Metallurgy, University'of New South Wales. Manuscript submitted April 3, 1970. METALLURGICAL TRANSACTIONS
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(min"1) Fig. 2---Strain rate dependence of ec and e x . 0.125 in. d i a m r o d s with a gage length of 0.8 in. The g r a i n s i z e w as 0.2 m m and all t e s t s w e r e conducted at r o o m t e m p e r a t u r e and constant c r o s s h e a d speed. T y p i c a l t r u e s t r e s s - s
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